A plasma treatment apparatus and method are provided, which have the capability of maintaining a stable discharge, achieving a sufficient plasma treatment, and reducing plasma temperature. In this apparatus, electrodes are arranged to define a discharge space therebetween, and a dielectric material is disposed at a discharge-space side of at least one of the electrodes. A voltage is applied between the electrodes, while a plasma generation gas being supplied into the discharge space, to develop the discharge in the discharge space under a pressure substantially equal to atmospheric pressure, and provide the plasma generated by the discharge from the discharge space. A waveform of the voltage applied between the electrodes is an alternating voltage waveform without rest period. At least one of rising and falling times of the alternating voltage waveform is 100 μsec or less. A repetition frequency is in a range of 0.5 to 1000 kHz. An electric-field intensity applied between the electrodes is in a range of 0.5 to 200 kV/cm.